More particularly, the present invention relates to a fuel flowmeter for being fed by a pump having an inlet and an outlet, said flowmeter comprising:                a metering valve having an inlet and an outlet, said valve being arranged downstream from the outlet of the pump;        a return circuit connecting the inlet of the metering valve to the inlet of the pump; and        a pressure regulator device comprising a movable valve member suitable for closing and opening the return circuit, a pressure difference detection surface fastened to the valve member and axially separating a first chamber in communication with the inlet of the metering valve from a second chamber in communication with the outlet from the metering valve, a first spring arranged in the second chamber while being fastened to the detection surface in such a manner as to exert axial thrust on the valve member in a direction tending to close the return circuit.        
One such flowmeter 10 that is already known from elsewhere is shown in FIG. 1. In known manner, the flowmeter is fed upstream by a pump 12 delivering a flow of fuel at a rate that is greater than the rate needed by the engine. The metering valve 14 is arranged between the pump and the injectors of the combustion chamber. This valve is designed to deliver a flow rate Q that is a function of the extent to which it is opened, which extent is controlled by a valve regulator system.
In order to obtain a flow rate that depends mainly on the extent to which the metering valve 14 is opened, the pressure difference between the outlet 14b and the inlet 14a of the metering valve must be maintained constant, at a predetermined value, or at least within a limited range. That is the role of the regulator device 16, generally referred to as a “delta-P” valve.
For this purpose, the regulator device 16 has two functions: its first function is to detect pressure variation between the outlet and the inlet of the metering valve 14. This first function is performed by the detection surface 18 that is constituted in this example by a diaphragm, and by the first spring 20, the diaphragm being capable of moving axially against the force of the first spring if the pressure difference is greater than the above-mentioned predetermined value.
Under such circumstances, the valve member 24 opens the return circuit 22, thereby allowing fuel to flow from the inlet to the metering valve 14a back to the inlet 12a of the pump 12, or increasing the rate of the return flow, thereby diminishing the flow rate through the metering valve 14. As a result, the pressure difference between the outlet and the inlet of the metering valve diminishes until it reaches the predetermined value, thereby causing the valve member 24 to close under drive from the first spring 20.
It is specified that the regulator device 16 is initially calibrated in such a manner that the return circuit 22 remains closed by the valve member 24 so long as the pressure difference is below the predetermined value.
Thus, the regulator device maintains an almost constant pressure difference (equal to the predetermined value) between the outlet and the inlet of the metering valve.
It is also specified that the action of the valve member 24 is generally progressive, thus enabling the valve member 24 to occupy an equilibrium position.
A drawback of this flowmeter arises in the event of the diaphragm being damaged. It can be understood that if the diaphragm is pierced or if it no longer achieves sealing between the first and second chambers, there is no longer a pressure difference between the first and second chambers of the regulator device, and as a result the force exerted on the valve member becomes equal solely to the force exerted by the first spring. This causes the return circuit 22 to be closed and leads to a significant and undesirable increase in the rate at which fuel is supplied to the engine.